Subtropical Storm Alberto made landfall around Laguna Beach, Florida with sustained winds of up to 45 mph Monday afternoon. It will now track inland, bringing heavy rain to much of the Eastern US throughout the incoming weekend. Some of the showers and thunderstorms associated with Alberto will lead to flash flooding and heavy rainfall in areas as deep tropical moisture is carried north. Flash Flood Watches are in effect for over half a dozen states in the Southeast and Mid-Atlantic. There are two separate areas where the higher precipitable water values (which indicate the water content in the atmosphere) are located: near and at the center of low pressure and the low pressure’s tail. This tail has been a feature with Alberto for days now, acting like a training line of heavy thunderstorms on the eastern flank of the storm.
Now on Wednesday the remnants of Alberto will move into the Great Lakes region. Some of the model guidance actually suggests the low pressure may restrengthen by a few millibars. Either way, heavy rain will remain the story. Rounds of rain and thunderstorms will be present across the western Ohio Valley into the western and central Great Lakes. Farther south and east, widely scattered showers and thunderstorms will be found again across the eastern third of the nation. Most activity will be in the Ohio Valley. A few of these storms may turn severe, and even a spotty tornado will be possible. The highest risk for flooding is near the center of Alberto tracks, from the western Ohio Valley to the Great Lakes. Flooding will also be possible in the Appalachians Mountains and Mid-Atlantic.
Scattered showers and thunderstorms will remain possible across this part of the country Wednesday night. Again, the most widespread activity will be near the low pressure in the Great Lakes region by this time period. We’re also going to see scattered showers and storms work into the northern Mid-Atlantic ahead of a warm front. This warm front will usher in warmer air and higher dew points, or more humidity.
On Thursday, we rinse and repeat. Yet another day of hit or miss showers and thunderstorms will be around, affecting the eastern third of the US, although storms will be very isolated in New England. Most of these storms will contain light to moderate rainfall. At this point, much of this convective activity will be driven by the daytime heating combined with the humidity and instability. We often call these “diurnal thunderstorms.”
Friday will be another similar day, although it looks to be the quietest day of the week. Most areas across the east will stay dry, with only a couple hit or miss showers hitting some areas briefly.
As the remnants of Alberto track farther east across southeastern Canada, some of its energy will transfer to a new, weak low pressure near the Mid-Atlantic coastline. This low pressure will not develop into a big coastal storm, but it will be slow-moving, keeping scattered showers around the Northeast and Mid-Atlantic regions into the weekend. Meanwhile, the Southeast to the Great Lakes and Ohio Valley will be in for a mostly dry Saturday. It’s not until Sunday when a new storm allows for precipitation to develop ahead of its cold front while tracking east. This will bring in a new period of rain to many portions of the East. Thankfully, the flooding risk will be much lower by this time period.